This invention relates to techniques for holding workpieces in a vacuum environment and, more particularly, to a method for holding a semiconductor wafer in a vacuum during lithographic pattern exposure in an integrated-circuit fabrication sequence.
Vacuum chucks are well known in the semiconductor art. They constitute versatile and reliable instrumentalities for holding semiconductor wafers during pattern delineation in photolithographic processes. By means of such chucks, wafers that inevitably exhibit some warpage can be firmly held during exposure in a manner to ensure that the wafer surface to be irradiated is maintained essentially flat. Such flatness is generally regarded as a prerequisite for achieving a high-resolution pattern.
In lithographic systems utilizing electron beams or ion beams, and even in some systems employing X-rays, the wafers to be irradiated during pattern delineation are contained in a vacuum environment. Of course, in such systems vacuum chucks unfortunately cannot be used to hold the wafers.
Mechanical clamping of the edges of a wafer is generally not sufficient by itself to ensure the surface flatness required for high-resolution patterning in a vacuum environment. And although electrostatic and magnetic chucks have been suggested for use in a vacuum, such chucks have generally not been viewed as attractive instrumentalities for use in manufacturing integrated-circuit devices.
Thus, efforts have been directed by workers skilled in the art aimed at trying to devise an improved workpiece holder for use in a vacuum environment. It was recognized that such efforts, if successful, would be of particular value in holding semiconductor wafers during the process of making integrated-circuit devices.